1. Field of the Invention
The invention relates to a plug-in combination of appliances for protection against overvoltages, comprising a socket-type lower part and one or several plug-in modules which accommodate the overvoltage protection elements, contact elements and contact counter elements which are respectively arranged in the lower part and in the plug-in module, as well as complementary guide rails or guide grooves for the controlled insertion or sliding-on and fixing of the respective plug-in module in accordance with the preamble of Claim 1.
2. Description of the Related Art
In many cases, overvoltage protection devices according to the state of the art are constructed as plug-in combination of appliances, comprising a lower part and a plug-in module.
Connecting terminals for contact-making of the electric conductors are disposed in the lower part, and corresponding receptacles for the plug-in modules to be inserted are provided therein. The lower part also houses elements which encompass one or several male contacts of the plug-in module, so that the desired mechanical and electrical contact as well as the appropriate seat of the plug-in module in the lower part is ensured.
The overvoltage protection elements proper, such as e.g. spark gaps, varistors, gas dischargers, or the like are located within the plug-in module.
The lower parts are often formed as U-shaped bodies, with the open legs of the U-shaped body laterally encompassing the plug-in module so that the plug-in module rests upon the connecting leg of the U-shaped parts. The lower part is further provided with receptacle elements at its installation side, which enable a so-called top-hat rail assembly.
The advantage of the briefly described separated functions between lower part and plug-in module is that the plug-in module may be removed for inspection and maintenance work without the necessity to open the connecting terminal or to disconnect the respective system from the supply, respectively.
The removed and separated plug-in module may then be examined remote from the electric system by means of special testing devices, and replaced or reassembled, as the case may be.
With respect to the state of the art, reference is made e.g. to DE 36 39 533 C2, DE 295 19 313 U1, DE 100 01 667 C1, and DE 20 2004 006 227 U1.
As a special problem attention should be paid to the fact that in the course of designing the male contact arrangement between lower part and plug-in module, this contact is to be designed for the surge current flowing through said contact in the discharge case with wave forms 10/350 μs and 8/20 μs or the mains frequency short circuit current, respectively.
In particular in overvoltage lightning current arresters as they are demanded in the market, partly considerable surge currents of up to 100 kA have to be carried several times via these contacts in such a manner that nearly no contact erosion or wear occurs. The relevant tests are specified in the product standards for overvoltage protection devices.
In order to reliably control surge currents of such magnitude, a very high contact force between the individual contact elements has to be selected. The consequence is that the plug-in modules according to the state of the art can be removed with considerable force applied and in most cases with the aid of a special tool only. Thus, an additional tool is required which means a considerable drawback for the use of the devices. There is also an additional potential hazard in that when handling the tool, an arcing fault may be caused unintentionally within the arrester with the resulting danger for humans and systems.
In cases where the contact force between the contact elements is designed lower, the removal of the plug-in modules may be facilitated, but there is a risk that under the influence of the effects of electrodynamic forces during the surge current, the plug-in module may unintentionally come free from the lower part so that a proper overall function of the device without providing for additional protective means is no longer ensured.